In the field of identification, labeling is commonly employed. One common form of the label consists of a (i) middle or substrate layer, e.g., film, foil, nonwoven such as Tyvek® (spun-bonded polyolefin), synthetic paper such as Valeron®, or paper, (ii) top or indicia layer providing the identification, e.g., ink, pigment, etc., and (iii) bottom or adhesive layer for attaching the label to the surface of an object. Many types of adhesives are available for use on a label, e.g., pressure-sensitive adhesives (PSAs), hot melt adhesives and the like, but PSAs are widely used because they allow fast and convenient attachment of the label to an object.
As convenient as PSA-bearing labels are, they are not without their limitations. For example, their use in harsh environments is of limited value. Under conditions of high heat (or extreme cold), elevated or reduced pressure and/or exposure to various solvents, particularly over extended periods of time, the PSA can lose its ability to bind the label to the object.
One such case is in the field of providing identification for tissue cassettes. Tissue cassettes are typically made of a thermoplastic material, and they are designed to hold biological tissue specimens while the specimen is subjected to dehydration followed by encapsulation in wax. The dehydration process requires exposure to a range of solvents such as formalin, ethanol or xylene. This is followed by embedding the dehydrated specimen in hot wax (e.g., molten paraffin). These processes can last for hours and can include exposure to heat and vacuum. Notwithstanding the wide range of PSAs available, e.g., acrylates, tackified natural and synthetic rubbers, silicones and urethanes, none have shown resistance to the complete range of conditions to which a tissue cassette is typically exposed.
As such, PSAs are generally unsuitable for reliable attachment of identification labels to tissue cassettes and, for that matter, to many consumer and industrial process containers that are also exposed to harsh environmental conditions, such as those used in the food and dairy industries, or those used for storage of hazardous materials, or those used in subzero storage (where many PSAs lose their adhesive properties). Moreover, PSAs can provide inadequate adhesion in those situations where the substrate is not exposed to harsh environmental conditions, but where the surface of the substrate is too rough or textured to allow for good adhesion between it and the label.
Aside from the various forms of adhesive attachment, various forms of mechanical attachment are known. For example, the use of staples, pins and other mechanical fasteners is common, although problematic, because the fasteners interfere with the handling of the cassette. Moreover, the design and construction of the label and substrate often do not lend themselves for use with mechanical fasteners.